Molecular motor proteins such as Myosin V, Dynein or Kinesin are no ratchets,
at least not with a
ashing asymmetric potential; the crucial asymmetry is in the
dynamical activity. We make that explicit in terms of a simple Markov model, emphasizing
the kinetic (and non-thermodynamic) aspects of stochastic transport. The
analysis shows the presence of a
uctuation symmetry in that part of the dynamical
activity which is antisymmetric under reversal of trailing and leading head of the
motor. The direction of the motor motion is determined by it.